The present invention concerns an improved method for making a plastics material yarn, particularly, but not exclusively, a dental floss.
Methods and materials used for the manufacture of dental floss are known to give reasonable results. However, there is a desire to improve the methods for manufacturing the floss and to find materials that will provide the desired properties in the floss.
According to one aspect of this invention there is provided a method of converting a plastics material into a yarn, comprising heating the plastics material to melt it, passing melted material through an extrusion die to form an extruded filament, and thereafter cooling the filament, wherein the plastics material is selected from the group comprising nylon, polyesters, polyethylene, polyvinyl chloride, polyphenylene sulphite, polystyrene.
The method may further include the step of passing the extruded filament through a draw roller assembly while elevating the temperature of the filament. The filament may be heated after exiting from the draw roller assembly.
The method may further include the step of passing the extruded filament through a plurality of draw roller assemblies whereby the temperature of the filament is elevated at least one of the assemblies. The filament may be heated after exiting from at least one of the draw roller assemblies.
According to another aspect of the present invention there is provided a method of converting a plastics material into a yarn the plastics material being selected from the group comprising nylon, polyesters, polyethylene, polyvinyl chloride, polyphenylene sulphide, polystyrene, the method comprising heating the material to melt it, pumping melted material through an extrusion die to form an extruded filament, cooling the extruded filament, passing the extruded filament through a first draw roller assembly while elevating the temperature of the filament, heating the filament in a heating zone as it exits from the first draw roller assembly and, thereafter, passing the filament through a second draw roller assembly operating at a different linear speed than the first draw roller assembly and spooling the filament exiting the second draw roller assembly.
Means may be included for pumping the material through the extrusion die. The pumping means may be a metering pump which may operate in the region of substantially 3 to substantially 18 rpm. preferably substantially 3 to substantially 5 rpm. In one embodiment, the metering pump may operate at substantial 7 to substantially 6 rpm. In another embodiment, the pump may operate at substantially 7 rpm. In a third embodiment the pump may operate at substantially 5 to substantially 4 rpm.
The plastics material may include Silica. Preferably, the silica is added in the form of particles. Preferably, silica is added to the material in an amount of 0 to substantially 25% wt/wt, suitably substantially 1 to substantially 5%. The silica may be added to the material prior to or during heating thereof. The silica may be a coloured silica.
The plastics material may include a silicone. The silicone may be linear polydimethyl silicone, suitably one sold by Dow Corning under the designation MB50-001 SILICONE MASTERBATCH. The silicone may be added in an amount 0 to substantially 50% wt/wt, preferably 0 to substantially 25% wt/wt, more preferably substantially 10 to substantially 15% wt/wt.
The material may further include polytetrafluroethylene (PTFE), for example, in an amount of substantially 5 to substantially 10% wt/wt.
The material may include a rubberising agent. The agent may be, for example a product sold under the trade mark ADFLEX. Alternatively, the agent may be any other similar product. The rubberising agent may be added to the material in an amount 0 to substantially 70% wt/wt, preferably 0 to substantially 40% wt/wt. The use of the rubberising agent has the effect of rendering to the gain a more rubbery texture, which can be advantageous when the yarn is to be used as a dental floss.
In the first embodiment, the rollers in the first heated draw roller assembly are rotating such as to impart to the filament a speed which may lie within the range 0 to substantially 200 m per minute, preferably within the range substantially 10 to substantially 50 m per minute. More preferably it is substantially 20 m per minute.
The temperature of the rollers in the first heated draw roller assembly of the first embodiment may lie within the range 0 to substantially 200xc2x0 C., preferably within the range substantially 80 to substantially 160xc2x0 C. More preferably it is substantially 105xc2x0 C. The temperature in the heating zone at the exit from the first draw roller assembly may lie within the range 0 to substantially 200xc2x0 C., preferably within the range substantially 80 to substantially 140xc2x0 C. More preferably it is substantially 120xc2x0 C.
Preferably the second draw roller assembly operates at a higher speed than the first draw roller assembly. In a first embodiment of the invention the second draw roller assembly is heated.
The temperature of the rollers in the second heated draw roller assembly of the first embodiment may lie within the range 0 to substantially 200xc2x0 C., preferably within the range substantially 60 to substantially 90xc2x0 C. More preferably it is substantially 70xc2x0 C.
The rollers of the second heated draw roller assembly of the first embodiment are rotating such as to impart to the filament a speed which may lie within the range 0 to 1000 m per minute, preferably with the range substantially 50 to substantially 250 m per minute. More preferably it is substantially 95 to substantially 100 m per minute.
In a second embodiment, the filament may be passed through an intermediate draw roller assembly arranged downstream of the first draw roller assembly and upstream of the second draw roller assembly.
In the second embodiment, the extruded filament may, be further heated in a second heating zone as the filament exits the intermediate draw roller assembly.
In the second embodiment, the rollers in the first draw roller assembly are rotating such as to impart to the filament a speed which may lie within the range of substantially 5 to substantially 50 m per minute, conveniently substantially 20 m per minute.
Preferably, the first draw roller assembly of the second embodiment comprises a plurality of rollers, conveniently five. The temperature of at least one of the rollers in the fire draw roller assembly of the second embodiment may lie in the range of substantially 50 to substantially 130xc2x0 C., conveniently 95 to substantially 110xc2x0 C., preferably substantially 105xc2x0 C. Conveniently the roller of the first draw roller assembly arranged furthest downstream thereof is heated. Preferably, the roller immediately upstream of said furthest downstream roller is also heated.
The temperature of the first mentioned heating zone at the exit from the first draw roller assembly of the second embodiment may lie in the range of substantially 50 to substantially 180xc2x0 C., conveniently substantially 115 to substantially 175xc2x0 C., preferably substantially 120xc2x0 C.
The temperature of the second heating zone at the exit from the intermediate draw roller assembly may lie in the range of substantially 50 to substantially 180xc2x0 C., suitably, substantially 100 to substantially 150xc2x0 C. conveniently substantially 140xc2x0 C.
The intermediate draw roller assembly may comprise a plurality of rollers, conveniently five. The rollers in the intermediate draw roller assembly are rotating such as to impart to the filament a speed which may lie in the range substantially 5 to substantially 250 m per minute, conveniently substantially 70 to substantially 175 m per minute, preferably substantially 70 or substantially 75 m per minute. Preferably, the temperature of at least one of the rollers of the intermediate draw roller assembly lies in the range of substantially 50 to substantially 150xc2x0 C., conveniently substantially 75 to substantially 125xc2x0 C., preferably substantially 100xc2x0 C.
The second draw roller assembly in the second embodiment may comprise a plurality of rollers, conveniently five. The rollers in the second draw roller assembly are rotating such as to impart to the filament a speed which may lie in the range substantially 50 to substantially 150 m per minute, conveniently substantially 95 to substantially 100 m or substantially 160 m per minute, preferably substantially 95 or substantially 100 m per minute.
The extruded filament may be cooled as it passes through the second draw roller assembly of the second embodiment. At least one of the rollers of the second draw roller assembly is at a temperature in the range substantially 50 to substantially 100xc2x0 C., conveniently substantially 60 to substantially 80xc2x0 C., preferably substantially 70xc2x0 C. Conveniently, the roller of the second draw roller assembly arranged furthest downstream thereof is cooled. Preferably, the roller immediately upstream of said furthest downstream roller is also cooled.
In one embodiment, flattening means is provided to flatten the filament. The flattening means may comprise at least one roller, and preferably a pair of flattening rollers between which the filament can pass. The flattening rollers are conveniently arranged to impart to the filament a thickness in the region of substantially 0.03 to substantially 0.15 mm, preferably substantially 0.05 to substantially 0.075 mm. Prior to passing through the flattening means the filament may have a thickness of substantially 0.095 mm. The flattening means preferably operates at a pressure in the range of 0 to substantially 200 psi.
Preferably, the flattening means acts to bilaterally orient the molecules in the filament, thereby providing improved lateral strength.
Preferably the filament is extruded in a generally downward direction from the extruder.
Preferably the extruded filament is cooled in a water bath. Preferably the temperature of the water in the bath is controlled.
Preferably the height of the water bath is adjustable to regulate the cross-section of the extruded filament.
Preferably the filament, as it leaves the extruder, takes the form of the extruding die which is generally rectangular in shape having radiused corners.
Preferably the dimensions of the extruder die are substantially 3 mm to substantially 15 mxc3x97substantially 0.25 mm to substantially 0.75 mm, more preferably substantially 12 mmxc3x97substantially 0.5 mm.
The flow rate of melted granules through the extruder may lie within the range substantially 2 to substantially 12 g per min.
The temperature of the melted granules may lie in the range substantially 200 to substantially 350xc2x0 C., preferably within the range substantially 250 to substantially 300xc2x0 C., more preferably substantially 280xc2x0 C.
Preferably the extruder pressure lies within the range substantially 600 to substantially 1400 psi. Preferably it is substantially 1000 psi. Preferably the speed of the metering pump feeding the molten granules to the extrusion die is substantially 1 to substantially 18 revs per minute, preferably substantially 2 to substantially 8 revs per minute. More preferably it is in the region of substantially 3 to substantially 5 revs per minute.
The water temperature within the cooling bath may be substantially 5 to substantially 50xc2x0 C., preferably substantially 10 to substantially 40xc2x0 C. More preferably it is substantially 35xc2x0 C.
The distance between the exit from the extrusion die and the water level in the cooling bath may lie within the range substantially 2 to substantially 40 mm, preferably substantially 2 to substantially 15 mm. In one embodiment, the distance is substantially 10 mm. More preferably it is in the range of substantially 5 to substantially 10 mm.
The depth of the water within the cooling bath may lie within the range substantially 0.1 to substantially 50 cm, preferably within the range substantially 10 to substantially 20 cm. More preferably it is substantially 15 cm.
The speed of the spooling assembly may lie within the range 0 to substantially 1000 m per minute, preferably within the range substantially 50 to substantially 250 m per minute. More preferably it is substantially 80 m per minute.
Where the material is a polyester, it may be polybutylene terephthalate.
According to another aspect of the present invention there is provided a yarn manufactured in accordance with the method described above.
In a first embodiment, the plastics material yarn may be manufactured by a method comprising heating to a temperature within the range substantially 200 to substantially 300xc2x0 C. granules of a plastics material, causing the melted granules to flow to an extrusion metering pump at a rate lying within the range substantially 2 to substantially 12 g per min, passing the melted material through the extrusion metering pump operating it at a speed within the range substantially 1 to substantially 18 revs per minute to create an extrusion pressure lying within the range substantially 600 to substantially 1400 psi, extruding the material through a die and guiding the extruded filament into a bath located between substantially 2 and substantially 40 mm below the exit from the extruder die and containing a cooling fluid, for example water, at a temperature lying within the range substantially 5 to substantially 50xc2x0 C., passing extruded filament from the water bath to a first heated draw roller assembly where the rollers are heated to a temperature of between 0 to substantially 200xc2x0 C. and pass filament therethrough at a speed lying within the range 0 to substantially 200 m per minute, heating the filament exiting from the first draw roller assembly in a heating zone to a temperature lying within the range 0 to substantially 200xc2x0 C. passing the material through a second heated draw roller assembly where the rollers are heated to a temperature of between 0 to substantially 200xc2x0 C. and passing the yarn therethrough at a speed of between 0 to substantially 1000 m per minute and spooling filament exiting from the second heated draw roller assembly at a speed of between 0 to substantially 1000 m per minute.
In a second embodiment, the plastics material yarn may be manufactured by a method comprising heating to a temperature within the range of substantially 200 to substantially 300xc2x0 C. granules of a plastics material, causing the melted granules to flow to an extrusion metering pump, passing the melted material through the pump and extruding the material through a die into a bath located between substantially 2 and substantially 40 mm below the exit of the extruder die and containing a cooling fluid, for example water at a temperature lying within the range of substantially 5 to substantially 50xc2x0 C., passing the extruded filament from the bath to a first heated draw roller assembly where at least one of the rollers are heated to a temperature lying in the range of substantially 50 to substantially 100xc2x0 C., and passing the filament therethrough at a speed lying within the range of substantially 15 to substantially 50 m per minute, heating the filament exiting from the first draw roller assembly in a first heating zone to a temperature lying in the range of substantially 100 to substantially 135xc2x0 C., passing the filament through an intermediate draw roller assembly at a speed lying within the range of substantially 150 to substantially 150 m per minute, heating the filament exiting from the intermediate draw roller assembly in a second heating zone to a temperature lying in the range of substantially 100 to substantially 150xc2x0 C., passing the filament through a second draw roller assembly where at least one of the rollers is cooled to a temperature lying in the range of substantially 50 to substantially 100xc2x0 C., and spooling the filament exiting from the second draw roller assembly.
According to another aspect of the invention there is provided a plastics material yarn having a width in the range of substantially 0.5 to substantially 4 mm, and a decitex in the range of substantially 400 to substantially 1500, wherein the plastics material is selected from the group comprising nylon, polyesters, polyethylene, polyvinyl chloride, polyphenylene sulphide, polystyrene.
Preferably, the width of the yarn is in the range of substantially 0.5 to substantially 2 mm. The thickness of the yarn may be in the range of substantially 0.03 to substantially 0.15 mm.
Preferably, the tensile strength of the yarn is in the range of substantially 12 to substantially 50N., more preferably substantially 15 to substantially 30N. The width of the yarn may be in the range of substantially 0.5 to substantially 2 mm, suitably substantially 0.6 to substantially 1.5 m. The decitex of the yarn may be in the range of substantially 550 to substantially 1000.
The plastics material may include a silicone. The silicone may be linear polydimethyl silicone, suitably one sold by Dow Corning under the designation MB50-001 SILICONE MASTERBATCH. The silicone may be added in an amount 0 to substantially 50% wt/wt, preferably 0 to substantially 25% wt/wt, more preferably substantially 10 to substantially 15% wt/wt.
The material may include PTFE, for example in an amount of substantially 5 to substantially 10% wt/wt.
The material may include silica, which may be in the form of particles. Preferably, the silica comprises substantially 1 to substantially 5% wt/wt of the material. The silica may be a coloured silica.
The material may include a rubberising agent. The agent may be, for example a product sold under the trade mark ADFLEX. Alternatively, the agent may be any other similar product. The rubberising agent may be added to the material in an amount 0 to substantially 70% wt/wt, preferably 0 to substantially 40% wt/wt. The use of the rubberising agent has the effect of rendering to the gain a more rubbery texture, which can be advantageous when the yarn is to be used as a dental floss.
The material may include a colouring, for example Titanium dioxde. The material may include from 0 to substantially 55wt/wt of said colouring, preferably substantially 1% wt/wt.
Where the material is polyester, it may comprise polybutylene terephthalate.
According to another aspect of this invention there is provided apparatus for converting a plastics material into a yarn, the apparatus comprising means for melting the material, means for pumping melted material through an extrusion die to form an extruded filament, means for cooling the extruded filament, a first draw roller assembly to draw the extruded filament therethrough, heating means to heat at least one of the rollers of said first draw roller assembly, a heating zone arranged at the exit of the first draw roller assembly to heat the extruded filament exiting from said first draw roller assembly, a second draw roller assembly operating at a different linear speed to the first draw roller assembly, and spooling means for spooling the filament exiting from the second draw roller assembly.
In a first embodiment, the rollers in the first heated draw roller assembly are rotating such as to impart to the filament a speed which may lie within the range 0 to substantially 200 m per minute, preferably within the range substantially 10 to substantially 50 m per minute. More preferably it is substantially 20 m per minute.
The temperature of the rollers in the first heated draw roller assembly of the first embodiment may lie within the range 0 to substantially 200xc2x0 C., preferably within the range substantially 80 to substantially 160xc2x0 C. More preferably it is substantially 105xc2x0 C. The temperature in the heating zone at the exit from the first draw roller assembly may lie within the range 0 to substantially 200xc2x0 C., preferably within the range substantially 80 to substantially 140xc2x0 C. More preferably it is substantially 120xc2x0 C.
Preferably the second draw roller assembly operates at a higher speed than the first draw roller assembly. In the first embodiment of the invention the second draw roller assembly may be heated.
The temperature of the rollers in the second heated draw roller assembly of the first embodiment may lie within the range 0 to substantially 200xc2x0 C., preferably within the range substantially 60 to substantially 90xc2x0 C. More preferably it is substantially 70xc2x0 C.
The rollers of the second heated draw roller assembly of the first embodiment are rotating such as to impart to the filament a speed which may lie within the range 0 to substantially 1000 m per minute, preferably within the range substantially 50 to substantially 250 m per minute. More preferably it is substantially 95 to substantially 100 m per minute.
In a second embodiment, the apparatus may include an intermediate draw roller assembly arranged downstream of the first draw roller assembly and upstream of the second draw roller assembly.
In the second embodiment the apparatus may include a second heating zone to heat the filament, the second heating zone being arranged at the exit of the intermediate draw roller assembly. Conveniently, intermediate draw roller assembly is substantially unheated. The temperature at the second heating zone is preferably in the range of substantially 50 to substantially 180xc2x0 C.
In the second embodiment, the rollers in the first draw roller assembly are rotating such as to impart to the filament a speed which may lie within the range of substantially 15 to substantially 50 m per minute, conveniently substantially 20 m per minute.
Preferably, the first draw roller assembly of the second embodiment comprises a plurality of rollers, conveniently five. The temperature of at least one of the rollers in the first draw roller assembly of the second embodiment may lie in the range of substantially 50 to substantially 130xc2x0 C., conveniently substantially 95 to substantially 110xc2x0 C. Conveniently the roller of the first draw roller assembly arranged furthest downstream thereof is heated. Preferably, the roller immediately upstream of said furthest downstream roller is also heated.
The temperature of the first mentioned heating zone at the exit from the first draw roller assembly of the second embodiment may lie in the range of substantially 50 to substantially 180xc2x0 C., conveniently substantially 115 to substantially 175xc2x0 C., preferably substantially 120xc2x0 C.
The temperature of the second heating zone at the exit from the intermediate draw roller assembly may lie in the range of substantially 50 to substantially 180xc2x0 C., suitably substantially 100 to substantially 150xc2x0 C., conveniently substantially 140xc2x0 C.
The intermediate draw roller assembly may comprise a plurality of rollers, conveniently five. The rollers in the intermediate draw roller assembly are rotating such as to impart to the filament a speed which may lie in the range substantially 50 to substantially 150 m per minute, conveniently substantially 70 to substantially 175 m per minute, preferably substantially 70 or substantially 75 m per minute. Preferably, the temperature of at least one of the rollers of the intermediate draw roller assembly lies in the range of substantially 50 to substantially 150xc2x0 C., conveniently substantially 75 to substantially 125xc2x0 C., preferably substantially 100xc2x0 C.
The second draw roller assembly in the second embodiment may comprise a plurality of rollers, conveniently five. The rollers in the second draw roller assembly are preferably rotating such as to impart to the filament a speed which may lie in the range substantially 5 to substantially 250 m per minute, suitably substantially 100 to substantially 250 m per minute, conveniently substantially 95 to substantially 100 m per minute, preferably substantially 95 or substantially 100 m per minute.
The second draw roller assembly of the second embodiment may be heated to a temperature below that of the intermediate draw roller assembly. At least one of the rollers of the second draw roller assembly is at a temperature in the range substantially 50 to substantially 100xc2x0 C., conveniently substantially 60 to substantially 80xc2x0 C. Preferably substantially 70xc2x0 C. Conveniently, the roller of the second draw roller assembly arranged furthest downstream thereof is cooled. Preferably, the roller immediately upstream of said furthest downstream roller is also cooled.
In one embodiment, flattening means is provided to flatten the filament. Preferably, the flattening means comprises at least one roller, and preferably a pair of flattening rollers between which the filament can pass. The flattening rollers are conveniently arranged to impart to the filament a thickness in the region of substantially 0.03 to substantially 0.15 mm, preferably substantially 0.05 to substantially 0.075 mm. Prior to passing through the flattening means the filament may have a thickness of substantially 0.095 mm.
Preferably, the flattening means acts to bilaterally orient the molecules in the filament, thereby providing improved lateral strength.
Preferably the filament is extruded in a generally downward direction from the extruder.
Preferably the cooling means is a water bath. Preferably the temperature of the water in the bath is controlled.
Preferably the height of the water bath is adjustable to regulate the cross-section of the extruded filament.
The flow rate of melted granules through the extruder may lie within the range substantially 2 to substantially 12 g per min.
The melting means may be adapted to heat the material to a temperature in the range substantially 200 to substantially 350xc2x0 C., preferably within the range substantially 250 to substantially 300xc2x0 C.
Preferably the extruder pressure lies within the range substantially 600 to substantially 1400 psi. Preferably it is substantially 1000 psi. Preferably the speed of the metering pump feeding the molten granules to the extrusion die is 1 to 18 revs per minutes preferably substantially 2 to substantially 8 revs per minute. More preferably it is in the region of substantially 3 to substantially 5 revs per minute.
The water temperature within the cooling bath may be substantially 5 to substantially 500xc2x0 C., preferably substantially 10 to substantially 40xc2x0 C. More preferably it is substantially 35xc2x0 C.
The distance between the exit from the extrusion die and the water level in the cooling bath may lie within the range substantially 2 to substantially 40 mm, preferably substantially 2 to substantially 15 mm. More preferably it is in the range of substantially 5 to substantially 10 mm. In one embodiment, the distance is substantially 10 mm.
When a dental floss has to be formed, the distance between the extrusion die and the water level may lie within the range substantially 2 to substantially 15 mm. More preferably it is substantially 10 mm. The depth of the water within the cooling bath may lie within the range substantially 0.1 to substantially 50 cm, preferably within the range substantially 10 to substantially 20 cm. More preferably it is substantially 15 cm.
The speed of the spooling assembly may lie within the range 0 to substantially 1000 m per minute, preferably within the range substantially 50 to substantially 250 m per minute. More preferably it is substantially 80 m per minute.